1. Field of the Invention
This invention relates to connectors on printed circuit boards and, more particularly, to apparatus providing a socket for a number of removable peripheral devices including both memory devices and input output devices.
2. History of the Prior Art
One of the most rapidly growing markets for computer systems is the portable computer market. In the last few years, portable computers have become more and more powerful while at the same time they have become smaller and lighter. As a part of this changing market, the various components of which a computer is constructed have become smaller and lighter while their ability to handle more and more data has increased. An important way in which this has been accomplished has been the reduction in physical size with the increase in data handling capacity of electro-mechanical hard disk drives (hereinafter referred to as rotating hard drives). Such rotating hard drives are very useful and have become almost a necessity to the operation of personal computers, especially portable computers.
However, such rotating hard drives do have their drawbacks. They are relatively heavy and increase the weight of a computer, especially a portable computer, significantly. Rotating hard drives draw a substantial amount of electrical power. In a portable computer this power is provided by batteries with limited operational lives. More importantly, rotating hard drives are very susceptible to shock. A rotating hard drive in a portable computer which is dropped is quite likely to cease functioning with a catastrophic loss of data.
Recently, other forms of data storage devices have begun to replace rotating hard drives in portable computers. For example, flat memory cards (about the size of a credit card) mounting an array of memory devices such as EPROM, EEPROM, SRAM, or flash EEPROM memory devices have been used as fixed storage for application programs. Such flat "solid state disks" supplement or eliminate the need for a portable computer to access a rotating hard drive during operation of the program. This makes the program run faster. Such solid state disks are light in weight and occupy very little space. More importantly, they are especially rugged and will withstand repeated drops each of which would destroy a typical rotating hard drive. If the rotating hard drive is eliminated, the portable computer is much more tolerant of shock. A flat memory card carrying data or an application program is typically connected to the computer through a socketing arrangement which protects the card and allows cards carrying different application programs or data to be interchanged with one another. One such memory card is described in U.S. patent application Ser. No. 07/861,013, entitled A FLASH MEMORY CARD WITH A READ/BUSY MASK REGISTER AND A READY/BUSY MODE REGISTER, Robinson et al, filed Mar. 31, 1992, and assigned to the assignee of the present invention.
Another group of devices which is especially important to portable computers includes peripheral input/output devices such as modems, facsimile machines, or local area networks. A modem, for example, allows a user of a portable computer to correspond with other computers using the telephone lines. It provides access to all of the data available at a base office without the need to store that data in a portable computer. Consequently, the reduction in size of modems has proceeded at the same pace as has the reduction in size of hard disks. Typically, the electronics of a modem are arranged on an internal board within the computer. Some arrangements provide a separate portable modem which may be carried along and connected to a portable computer when needed. Some modems have been designed recently which plug into sockets recessed within the body of a portable computer.
Historically, each of the aforementioned useful peripheral devices has required its own interface circuitry for connecting to the internal circuitry of a portable computer. This required both interface circuitry and a socket for each device. Of late, apparatus has been devised which allows some of these various forms of computer components to be plugged into the same socket of a computer thereby reducing the space needed within the portable computer. For example, an international standard which defines the physical and electrical interface specifications for the interchangeability of memory and input/output cards was introduced by Personal Computer Memory Card International Association (PCMCIA) jointly with the Japanese Electrical Industry Association (JEIDA) in September 1991. In addition, a specification referred to as an Exchangeable Card Architecture (ExCA) Specification, Dec. 20, 1991, has been issued by Intel Corporation of Santa Clara, Calif. This document describes specifications which manufacturers may use for devising interfaces which meet the requirements for insuring the interchangeability of memory and input/output cards for portable personal computers of different manufacturers. A socket designed to these specifications allows cards such as a modem and a flash memory to be attached, used, and removed interchangeably in the same socket. Such apparatus includes at least one socket recessed into the computer so that the devices connected are protected by the body of the computer and interface circuitry for each of the components to be connected. This new apparatus has offered a great increase in the usefulness of a typical portable computer. Unfortunately, the circuitry and hardware needed to allow this multiple use of the socket is larger than desirable and takes up a great deal of space within a portable computer. It is very desirable that the size of this space be reduced.